This invention relates to a container or tank for the storage or transportation of large volumes of bulk fluids at extremely low temperatures and in particular relates to an improved internal thermal insulating structure for such a tank. In the past, many various types of insulated tanks for the shipping of cryogenic fluids have been proposed. The patent literature is exemplified by French Pat. No. 1,383,795 and U.S. Pat. Nos. 3,013,922; 3,122,043; 3,261,087; 3,400,849; 3,502,239; 3,548,453; and 3,655,086. However, in practice, essentially only two basic ship tank designs have been employed to any significantt extent, namely, a membrane tank design and a free-standing tank design. For an excellent discussion of the various types of ship tank designs, see the paper presented by Thomas et al. to the Society of Naval Architects and Marine Engineers, November 11-12, 1971, entitled, "LNG Carriers: The Current State of the Art".
One of the major considerations in the design of tanks having a rectilinear cross section, wherein the load is supported by and in direct contact with the insulation, particularly tanks for barge or ship transport of large volumes of cryogenic liquids, such as liquid natural gas, is to minimize the stress concentration at the corners and to strengthen the corner construction so that the high tensional and torsional loadings can be absorbed without failure. As is evident from the aforementioned prior art, the corner construction has been quite complex and expensive due primarily to the extremely low operating temperatures and the wide temperature variations to which the construction is exposed.
Against this background, the present invention was developed.